Hydraulic servo valves can take on a variety of different forms including for example the electro-hydraulic servo type and those that feature multiple chambers, ports, valve lands, etc. The electro-hydraulic servo valve typically includes two or three stages of amplification. A three stage servo valve may have for example a first stage that converts electrical current to motion via a torque motor, a second stage that converts motion to hydraulic pressure via a projector jet and receiver, and a third stage that converts hydraulic pressure to flow via a spool valve. In a two stage servo valve, the hydraulic pressure intermediate stage may be eliminated and a linear motor may directly drive the spool. Electro-hydraulic servo valves may also or alternatively employ a piezo-electric actuator. The actuator may be coupled to a cantilever to increase the range of motion of the actuator. All of these electro-hydraulic servo valves can have various disadvantages relative to certain applications. For example, as every stage of an electro-hydraulic servo valve is physically interconnected, analyzing and designing a multi stage servo valve can be complicated and time consuming. Moreover, manufacturing variations may compromise performance. And servo valves that utilize cantilever mechanisms may in some applications be impractical as they may experience excessive lateral displacement. Existing two stage designs that utilize a linear motor may tend to have lower performance than three stage designs, and so will tend to be larger and heavier for equivalent performance.
Some hydraulic servo valves may be configured to perform flow control, directional control, or pressure control, in which case they may incorporate for example a spool mechanism with various chambers, valve lands, supply and return ports, and work ports to realize particular performance characteristics. A typical application of a directional control valve may be to drive a double acting piston cylinder type actuator. The servo directional control valve can change the direction of hydraulic flow to either the extension side of the piston or the retraction side of the piston to respectively extend or retract the piston within the cylinder. These types of servo valves also suffer from various drawbacks relative to certain applications. For example, the particular configuration of the valve lands may limit the flexibility in control of the overlap and underlap capabilities of the servo valve.
Accordingly, there remains a need for further contributions in this area of technology.